Help: Update Sphinx versionadded directives for 3.27 release

Run the script:

    Utilities/Sphinx/update_versions.py --since v3.26.0 --overwrite

Manually remove directives added to new documentation of existing
environment variables.

Help/prop_tgt/AUTOGEN_USE_SYSTEM_INCLUDE.rst

@@ -1,6 +1,8 @@
 AUTOGEN_USE_SYSTEM_INCLUDE
 --------------------------
 
+.. versionadded:: 3.27
+
 ``AUTOGEN_USE_SYSTEM_INCLUDE`` is a boolean property that can be set
 on a target to indicate that the autogen target include directory should
 be added as a system include directory or normal include directory to the